Method for Manufacturing a Spark Plug and Spark Plug Manufactured Accordingly

ABSTRACT

Method for manufacturing a spark plug comprising an inner conductor, an insulator enclosing the inner conductor, a spark plug body enclosing the insulator, and two electrodes, the first electrode being a center electrode connected to the inner conductor in an electrically conductive manner, and the second electrode being a ground electrode connected to the spark plug body in an electrically conductive manner, with a separately prefabricated precious metal component positioned on one of the electrodes and connected to the electrode by way of resistance welding, and subsequently affixed by way of laser or electron beam welding, so that the precious metal component extends like a heel beyond the electrode surface next to the precious metal component. The precious metal component, a ball, is shaped by stamping after resistance welding and before laser or electron beam welding, wherein at least one region of the ball protruding from the electrode surface (is reshaped.

The present invention relates to a method for manufacturing a spark plugthat comprises an inner conductor, an insulator enclosing the innerconductor, a spark plug body enclosing the insulator, and twoelectrodes, of which the first electrode is a center electrode connectedto the inner conductor in an electrically conductive manner, and thesecond electrode is a ground electrode connected to the spark plug bodyin an electrically conductive manner, in which a separatelyprefabricated precious metal component is positioned on one of theelectrodes, is thereafter connected to the electrode by way ofresistance welding, and subsequently is affixed by way of laser orelectron beam welding, so that the precious metal component extends likea heel beyond the electrode surface next to the precious metalcomponent.

A method of this type is known from DE 196 41 856 B4. In the case of theknown method, a small precious metal plate having the shape of acylinder is used as the precious metal component. The precious metalplate is pressed into the electrode during resistance welding, therebyresulting in an overhanging section around an outer periphery of theprecious metal plate, which holds the precious metal plate on theelectrode. The overhanging section, which surrounds the precious metalcomponent in the manner of a collar, is then connected to the preciousmetal component by way of laser or electron beam welding. Given that theelectrode material is deformed around the outer periphery of theprecious metal plate into the shape of a section overhanging in themanner of a collar, it is necessary when performing laser or electronbeam welding to melt on a relatively large quantity of the electrodematerial, namely the entire section of the electrode material projectingin the manner of a collar, before a region of the precious metal platecan even be melted on. This procedure is laborious. In addition, thehandling of the precious metal component is relatively complex whenplacing and positioning on the electrode since care must be taken toorient the precious metal plate correctly.

The problem addressed by the invention is that of simplifying themanufacture of a spark plug.

The problem is solved in the case of the method of the initiallydescribed type by using a ball as the precious metal component, and byshaping the precious metal component by stamping after resistancewelding and before laser or electron beam welding, wherein at least oneregion of the ball protruding from the electrode surface is reshaped.

The new method simplifies the manufacture of a spark plug in a pluralityof ways. Due to the use of a spherical precious metal component as asemi-finished product, to be connected to the electrode, the step oforienting the precious metal component when placing and positioning theball on the electrode is eliminated entirely. The ball is symmetrical inall directions and can therefore be placed onto the electrode with anyorientation. As a result, placement and positioning on the electrode arevery simple. The handling of the spherical precious metal componentsbefore the positioning thereof on the electrode, in particular whensupplied and isolated in a device for manufacturing the spark plug, islikewise very simple. Balls can be manufactured very easily andeconomically.

A further advantage of the use of a ball as the precious metal componentis that the amount of material used for the precious metal component isminimized. The use of a ball makes it possible to fulfill the objectiveof using the precious metal component—namely that of protecting theelectrode in order to reduce wear on the spark plug—particularlysuccessfully using a very small quantity of precious metal. The preciousmetal component does not need to contain an excessive quantity ofprecious metal which subsequently does not help to protect the electrodeagainst wear.

The method according to the invention is very well suited for equippingthe ground electrode as well as the center electrode with a preciousmetal. Of course it is possible to also equip both electrodes of a sparkplug with a precious metal component.

A spark plug comprising a precious metal component projecting from theelectrode surface has the advantage that less voltage is required tocreate a spark. A projection relative to the surface of the electrodesurrounding the precious metal component is provided. Advantageously theprojection is designed like a heel or as a type of step. The projectingsurface of the precious metal component does not transition evenly intothe surface of the electrode. A shoulder is provided in the region ofthe transition of the projecting precious metal component into thesurface of the electrode. The shoulder is preferably step-shaped. It canbe slightly rounded. The precious metal component can comprise an edgein the rim region thereof, before the surface thereof transitions intothe electrode surface, to promote the creation of an arc.

The shaping of the precious metal component by stamping has theadvantage that the spherical ball surface is reshaped in a way that isoptimized for spark creation and the service life of the spark plug.Since the stamping is carried out after the resistance welding, thespherical precious metal component is already connected to the electrodeduring the stamping process, thereby ensuring that it will not lose itsposition.

It is advantageous for the ball to be shaped by stamping a compressionpunch that presses onto the ball in the direction of the electrode, andfor the region of the sphere projecting from the electrode surface tothereby be reshaped such that the precious metal component ultimatelyprojects from the electrode surface by a predefined height. Thepredefined height by which the precious metal component projects fromthe electrode surface next to the precious metal component is a setpointvalue that is selected on the basis of the desired properties of thespark plug, in particular in regard to ignition voltage and servicelife. The compression punch is advanced onto the electrode until thedesired height of the projecting precious metal component results. It isparticularly advantageous when a region of the ball that projects fromthe electrode surface is shaped by stamping into a shape of asubstantially planar surface, which in particular extends approximatelyparallel to the electrode surface. The formation of a substantiallyplanar surface out of the originally spherical ball surface creates anedge on the precious metal component that surrounds the substantiallyplanar surface and improves spark creation.

According to a further embodiment of the invention, it is advantageousfor a region of the ball projecting from the electrode surface to beshaped by stamping into the shape of a jacket surface of a cone, atruncated cone, or a cylinder. As a result, the precious metal componentprojects from the electrode surface particularly well in the form of aheel-like step. It is particularly advantageous when the precious metalcomponent in the region projecting from the electrode surface isreshaped as a truncated cone. A truncated cone enables good sparkformation given low spark voltage to be combined particularly well witha long service life, while simultaneously ensuring ease of manufactureby way of the stamping process.

According to a further embodiment it can be advantageous for a ridge tobe integrally formed during stamp-molding on that end of the conical orcylindrical region facing the electrode. In this manner, a ridge-shapedregion forms on the precious metal component, the diameter of which isgreater than that of the cylindrical or conical region. The ridge of theprecious metal component can be easily melted and connected to the basicmaterial of the electrode in the subsequent laser or electron beamwelding step. The result is a particularly secure connection of theprecious metal component to the electrode, which does not come looseeven in the presence of high stresses due to temperature fluctuations.

Advantageously, the compression punch used for shaping by stamping has apredefined shape in the region thereof that reshapes the ball, whichshape corresponds to the desired final form of the precious metalcomponent. The compression punch is shaped—in the region thereof thatreshapes the ball—as a “die” or a “header”, as it is known from thefield of riveting, to impart the desired shape of the finished preciousmetal component to the region of the ball projecting from the electrodesurface, preferably in one working step. The stamping process issimplified as a result.

Preferably a hollow welding electrode is used for the positioning andresistance welding of the ball, which positions the ball on the groundelectrode or the center electrode of the spark plug and welds itthereto. The tip of the welding electrode preferably has the shape of acalotte. A channel is disposed in the tip, to which a vacuum can beapplied to suction the ball onto the welding electrode. Using a weldingelectrode of this type, the ball can be removed from a magazine veryeasily and then positioned on the spark plug electrode, where it is thenresistance-welded directly.

To ensure good fixation of the precious metal component, it isadvantageous for the laser or electron beam to extend approximately at aright angle to the electrode surface during laser or electron beamwelding. As a result, the precious metal component shaped by stampingcan be connected to the electrode very easily around the entirecircumference thereof.

The invention furthermore relates to a spark plug that is manufacturedusing the method according to the invention. In regard to the spark plugit is preferably provided that the precious metal component projectsfrom the electrode surface next to the precious metal component by aheight of approximately 0.1 mm to 1.0 mm, particularly preferably by aheight of approximately 0.2 mm to 0.6 mm. Advantageously a region of theprecious metal component projecting from the electrode surface has adiameter of approximately 0.3 mm to 1.5 mm, which particularlypreferably lies in the range of approximately 0.4 mm to 1.0 mm.

The precious metal component is preferably composed of platinum or aplatinum alloy. A ball composed of platinum or a platinum alloy hassufficiently great ductility and is therefore particularly easy toreshape by way of the stamping process.

Further advantages and features of the invention will be apparent fromthe subsequent description of a few embodiments.

In the drawings:

FIG. 1 shows a partial depiction of a spark plug, in an enlarged andpartial cross-sectional view,

FIG. 2 shows a further enlarged subregion of the ground electrode of thespark plug depicted in FIG. 1 during resistance welding of a preciousmetal component,

FIG. 3 shows a view of the ground electrode similar to FIG. 2, duringshaping of the precious metal component by stamping,

FIG. 4 shows a view of the ground electrode similar to FIG. 2, duringlaser welding of the precious metal component,

FIG. 5 shows a view similar to FIG. 3, of a variant of shaping bystamping,

FIG. 6 shows a view of the variant of FIG. 5 during laser welding,

FIGS. 7 and 8 show depictions similar to FIGS. 5 and 6 of a furthervariant with a different shaping of the precious metal component.

Spark plug 1 shown in FIG. 1 contains an inner conductor 2 enclosed byan insulator 3. A spark plug body 4 which encloses insulator 3 andhouses it is provided. A thread 5 is provided on the outer surface ofspark plug body 4. The spark plug contains two electrodes 6 and 7. Firstelectrode 6 is a center electrode which is connected to inner conductor2 in an electrically conductive manner. Second electrode 7 is a groundelectrode which is connected to spark plug body 4 in an electricallyconductive manner. A precious metal component 8 is attached to centerelectrode 6, and a precious metal component 9 is attached to groundelectrode 7. Precious metal component 8 projects in a heel-like mannerhaving a height H from a surface 10 of electrode 6 in a region thatencloses the precious metal component 8. The precious metal component 9likewise projects from surface 11 of electrode 7 in a heel-like mannerhaving a height H. The ground electrode 7 is disposed above the centerelectrode 6 in the manner of a front electrode, so that precious metalcomponents 8 and 9 are separated by a distance A and form a spark gap.

Spark plug 1 can be inserted into an internal combustion engine by wayof thread 5 thereof in a manner known per se. The region of spark plug 1comprising electrodes 6 and 7 then extends into a combustion chamber ofthe internal combustion engine, where it can ignite a fuel-air mixture.

Ground electrode 7 is composed of a nickel alloy, at least in the regionof electrode surface 11 next to precious metal component 9. Groundelectrode 7 can comprise a jacket composed of a nickel alloy beingdisposed around a copper core 12. Precious metal components 8 and 9 arepreferably composed of platinum or a platinum alloy and form anchorpoints having a small surface area and inverse properties whichdetermine the voltage requirement and ignition site. The materialcombination of platinum/nickel ensures that the arc of the spark occurson the precious metal component composed of platinum. At that pointthere is a great work function, a low evaporation rate, and practicallyno oxidation. The further discharge of the spark in the arc and flowphase immediately transitions into the regions—which are designed assacrificial regions—of electrodes 6 and 7 which are composed of nickel,where a low work function is required. The effective spark lengththerefore increases relative to distance A between electrodes 6 and 7and promotes the combustion of the mixture in the combustion chamber ofthe internal combustion engine. The voltage required to create the sparkof spark plug 1 is determined by distance A, however. It can be reducedwithout impairing the combustion of the fuel mixture, thereby enablingthe voltage required by the spark plug to be reduced. The result thereofis an increased service life of spark plug 1.

Spark plug 1 is manufacturing using the method according to theinvention, wherein, in particular, precious metal component 9 isattached to ground electrode 7 in the manner according to the invention.The invention is described in the following with reference to theexample of attaching precious metal component 9 to ground electrode 7.Precious metal component 8 can be attached to center electrode 6 in ananalogous manner. A separate description will be omitted to preventrepetition. The manufacturing process is described in the following withreference to FIGS. 2 to 8. In those figures, the same referencecharacters are used to label parts that are the same as in FIG. 1.

In manufacturing spark plug 1, ground electrode 7 is provided withprecious metal component 9. A separately prefabricated ball 13 is usedfor precious metal component 9, as shown in FIG. 2. The separatelyprefabricated ball 13 can be removed from a magazine, which is notdepicted, using a hollow welding electrode 14, for example. Weldingelectrode 14 comprises a spherical calotte-shaped seat 15 for the ball14. A vacuum channel 16, which terminates in the region of recess 15, isprovided in the interior of hollow welding electrode 14. When a ball 13is removed from the magazine, a vacuum is applied to vacuum channel 16,and a ball 13 is suctioned onto calotte-shaped seat 15 and retainedthere. Using welding electrode 14, ball 13 is subsequently positioned onground electrode 7 and is connected to ground electrode 7 at the desiredpoint by way of resistance welding. Finally, welding electrode 14 islifted off of ball 13. This state is shown in FIG. 2.

After the resistance-welding process, ball 13 is shaped by stamping. Theshaping by stamping will be explained with reference to FIG. 3. Acompression punch 17 is provided, which is advanced toward ball 13 inthe direction of ground electrode 7, and so at least a region of theball 13 extending beyond the electrode surface 11 is shaped. Compressionpunch 17 is pressed onto ball 13 so far that precious metal component 9subsequently projects from electrode surface 11 by a predefined heightH. Finally, compression punch 17 is lifted off of precious metalcomponent 11. This state is shown in FIG. 3. The surface of preciousmetal component 9, which was originally spherical, is provided with aplanar surface 18 by way of stamping. An edge 19 is formed thatsurrounds planar surface 18. Planar surface 18 is oriented parallel toelectrode surface 11.

After shaping precious metal component 9 by stamping, it is affixed toground electrode 7 by way of laser beam welding, as depicted in FIG. 4.An alloy zone 20 thereby forms between precious metal component 9 andground electrode 7, in which the materials of precious metal components9 and electrode 7 mix. Precious metal component 9 is attached verysecurely to electrode 7 by way of alloy zone 20 and cannot becomedetached even in the presence of strong temperature fluctuations. Thelaser beam is indicated by arrows 21. During laser welding, laser beam21 is oriented such that it preferably extends at a right angle or atleast nearly at a right angle to electrode surface 11. Finished preciousmetal component 9, which projects outward in a heel-like manner,comprises a region having a diameter D and extending beyond electrodesurface 11.

A variant of the shape-molding of ball 13 is depicted in FIG. 5. Ball 13is reshaped into a shape that differs from that shown in FIG. 3. Inaddition to a planar surface 18, a region having a shape of a jacketsurface 22 of a truncated cone is provided on precious metal component 9depicted in FIG. 5. Planar surface 18 is delineated from jacket surface22 of the truncated cone by an edge 19. In addition, a ridge 23 isintegrally formed on the end of the conical region 22 facing theelectrode 7. The compression punch 17 shown in FIG. 5 has a predefinedshape in its region 24 which shapes the ball 13, the predefined shapecorresponding to the desired final shape of precious metal component 9having planar surface 18, conical surface 22, and ridge 23. The laserwelding of precious metal component 9, which has been shaped by stampingaccording to FIG. 5, is depicted in FIG. 6. Ridge 23 is melted usinglaser beam 21 and, together with the melted basic material of groundelectrode 7, forms alloy zone 20. Finished precious metal component 9extends beyond electrode surface 11 by a height H and has a diameter Din the projecting region. In a variant that is not depicted, jacketsurface 22 can be reshaped into a jacket surface of a cylinder.

A further variant of the shape of a precious metal component 9 is shownin FIGS. 7 and 8. In comparison to precious metal component 9 shown inFIG. 5, the precious metal component shown in FIG. 7 is reshaped into amore pointed shape. Planar surface 18 is reduced in size and conicalsurface 22 can have a smaller cone angle.

Particularly good results are obtained in all of the variants describedwhen height H is in the range 0.1 mm to 1.0 mm, in particular between0.2 mm and 0.6 mm. Diameter D can be in the range 0.3 mm to 1.5 mm,wherein a diameter of 0.4 mm to 1.0 mm is preferred.

REFERENCE CHARACTERS

-   1 Spark plug-   2 Inner conductor-   3 Insulator-   4 Spark plug body-   5 Thread-   6 Center electrode-   7 Ground electrode-   8 Precious metal component-   9 Precious metal component-   10 Electrode surface of the center electrode-   11 Electrode surface of the ground electrode-   12 Copper core-   13 Ball-   14 Welding electrode-   15 Seat-   16 Vacuum channel-   17 Compression punch-   18 Planar surface-   19 Edge-   20 Alloy zone-   21 Laser beam-   22 Jacket surface-   23 Ridge-   24 Shaping region of the compression punch-   A Distance-   D Diameter-   H Height

1. A method for manufacturing a spark plug comprising an innerconductor, an insulator enclosing the inner conductor, a spark plug bodyenclosing the insulator, and two electrodes, of which the firstelectrode is a center electrode connected to the inner conductor in anelectrically conductive manner, and the second electrode is a groundelectrode connected to the spark plug body in an electrically conductivemanner, in which a separately prefabricated precious metal component ispositioned on one of the electrodes, is thereafter connected to theelectrode by way of resistance welding, and is subsequently affixed byway of laser or electron beam welding, so that the precious metalcomponent extends like a heel beyond the electrode surface (10; 11) nextto the precious metal component, wherein a ball is used as the preciousmetal component, and shaping of the precious metal component by stampingis carried out after the resistance welding and before the laser orelectron beam welding, thereby reshaping at least a region of the ballprotruding from the electrode surface.
 2. The method according to claim1, wherein the ball is shaped by stamping using a compression punchwhich presses onto the ball in the direction of the electrode, therebyreshaping that region of the ball extending beyond the electrode surfacesuch that the precious metal component thereafter extends beyondelectrode surface by a predefined height.
 3. The method according toclaim 1, wherein a region of the ball extending beyond the electrodesurface is reshaped substantially into the shape of a planar surface. 4.The method according to claim 3, wherein the substantially planarsurface is formed approximately parallel to the electrode surface. 5.The method according to claim 1, wherein by said shaping by stamping aregion of the ball extending beyond the electrode surface is reshapedinto a shape of a jacket surface of a cone, of a truncated cone, or of acylinder.
 6. The method according to claim 5, wherein by said shaping bystamping a ridge is formed on that end of the conical or cylindricalregion facing the electrode carrying the conical or cylindrical region.7. The method according to claim 6, wherein the ridge is melted thereonin the subsequent laser or electron beam welding process.
 8. The methodaccording to claim 2, wherein the compression punch in the regionthereof that reshapes the ball has a predefined shape corresponding tothe desired final shape of the precious metal component.
 9. The methodaccording to claim 1, wherein a hollow welding electrode is used for thepositioning and resistance welding of the ball, which positions the ballon the ground electrode or on the center electrode, respectively, of thespark plug and welds it thereto.
 10. The method according to claim 1,wherein the laser or electron beam extends approximately perpendicularlyto the electrode surface during laser or electron beam welding.
 11. Aspark plug comprising an inner conductor, an insulator enclosing theinner conductor, a spark plug body enclosing the insulator, and twoelectrodes, of which the first electrode is a center electrode (6)connected to the inner conductor in an electrically conductive manner,and the second electrode is a ground electrode connected to the sparkplug body in an electrically conductive manner, in which a preciousmetal component is disposed on at least one of the electrodes andprojects like a heel beyond the electrode surface next to the preciousmetal component, wherein the spark plug is manufactured by a methodaccording to claim
 1. 12. The spark plug according to claim 11, whereinthe precious metal component projects beyond the electrode surface nextto the precious metal component by a height of 0.1 mm to 1.0 mm, inparticular 0.2 mm to 0.6 mm.
 13. The spark plug according to claim 11,wherein a region of the precious metal component projecting beyond theelectrode surface has a diameter of 0.3 mm to 1.5 mm, in particular 0.4mm to 1.0 mm.
 14. The spark plug according to claim 11, wherein theprecious metal component is composed of platinum or a platinum alloy.